This invention relates to a hydrometallurgical process for the extraction of copper from a copper sulphide containing concentrate, including mixed sulphide concentrates, in particular from chalcopyrite.
Generally, researchers have found that chalcopyrite tends to leach slowly and incompletely at lower temperatures (below 100xc2x0 C.) and that at very high temperatures (above 200xc2x0 C.) sulphur is fully oxidised to sulphate.
Total sulphur oxidation has the disadvantage of higher oxygen consumption (increasing operating costs), more by-product acid for neutralisation (increased requirement for limestone/lime) and more heat produced in the autoclave per unit concentrate treated (increased dilution cooling necessitates larger autoclaves).
At medium temperatures (approximately 150xc2x0 C.), copper extraction has generally been incomplete due either to xe2x80x9cpassivationxe2x80x9d of the chalcopyrite surface by a metal-polysulphide layer or due to partially reacted chalcopyrite becoming coated with liquid elemental sulphur. Liquid elemental sulphur may agglomerate resulting in the formation of coarse, difficult to handle particles, which create materials handling and slurry transport difficulties.
Previous attempts have been made at applying the well known zinc sulphide hydrometallurgical pressure leaching process to the recovery of copper from chalcopyrite concentrates, using surfactantsts such as a lignin derivative, a tannin compound such as quebracho, and orthophenylene diamine, to disperse the elemental sulphur formed and to subsequently render the copper extractable, This work demonstrated that the use of sulphur-dispersing surfactants employed in zinc processes cannot be straightforwardly extrapolated to the pressure leaching of copper sulphide concentrates, specifically chalcopyrite. Most of the surfactants tested were considered to decompose too rapidly to be beneficial and the best result was achieved with orthophenylene diamine, resulting in low copper extraction of 80% after 6 hours of pressure leaching. This approach to the treatment of chalcopyrite concentrates was therefore dismissed as being ineffective and has not been applied commercially.
At the present time therefore, despite extensive research conducted into the development of commercially viable hydrometallurgical processes for the extraction of copper from chalcopyrite, pyrometallurgical processes remain the technology of choice.
South African Patent No 96/1547 (equivalent to U.S. Pat. No 5,730,776) teaches a hydrometallurgical process for the extraction of copper from copper sulphide concentrates which includes dispersing finely divided sulphidic copper concentrate in a aqueous sulphuric acid solution to form a slurry, and adjusting the concentration of sulphuric acid whereby it is effective to provide a predetermined copper, iron and acid concentration in a final leach solution; providing an effective amount of finely divided particulate carbonaceous material, compatible with the acid sulphate leach solution, which is operative under the reaction conditions of the following oxidising reaction step, to inhibit the passivation of incompletely leached sulphide particles; reacting, with agitation, the slurry and carbonaceous material with free oxygen bearing gas in a pressure vessel at a temperature effective to produce substantially complete extraction of copper values from the sulphides as soluble copper sulphate and concurrent conversion of a substantial portion of sulphide sulphur associated with the copper values to elemental form; and separating the product leach solution containing the dissolved copper values from the solid residue. The use of surfactants was considered not to be commercially viable, due to decomposition during pressure leaching and the use of carbonaceous material is a key element in the process,
U.S. Pat. No 5,874,055 teaches a process for the extraction of copper from a sulphide copper ore or concentrate which comprises the steps of subjecting the ore or concentrate to pressure oxidation in the presence of oxygen and an acidic halide solution to obtain a resulting pressure oxidation slurry, and subjecting the slurry to a liquid/solid separation step to obtain a resulting pressure oxidation filtrate and a solid residue containing an insoluble basic copper sulphate salt, The pressure oxidation is conducted in the presence of a source of bisulphate or sulphate ions which is selected from the group consisting of sulphuric acid and a metal sulphate which hydrolyses in the acidic solution. The amount of source of bisulphate or sulphate ions which is added contains at least the stoichiornetric amount of sulphate or bisulphate ions required to produce the basic copper sulphate salt, less the amount of sulphate generated in situ in the pressure oxidation.
The process further comprises the steps of recyling the pressure oxidation filtrate to the pressure oxidation; leaching the solid residue containing the basic copper sulphate salt in a second leaching with an acidic sulphate solution to dissolve the basic copper salt to produce a leach liquor containing copper sulphate in solution and a resulting solid residue; separating the leach liquor from the solid residue; subjecting the leach liquor to a solvent extraction process to produce copper concentrate solution and a raffinate; and recycling the raffinate to the second leaching.
It is to be noted that this process requires the use of an acidic halide solution in the pressure oxidation stage, and that the copper is recovered from the pressure oxidation stage in the form of an insoluble basic copper sulphate salt.
In an article entitled xe2x80x9cEffect of sulfur-dispersing surfactants on the oxidation pressure leaching of chalcopyritexe2x80x9d by Hackl et al, proceedings of COPPER 95-COBRE 95-COBRE 95 International Congress, Volume 3, Electrorefining and Hydrometallurgy of Copper, The Metallurgical Society of CIM, Montreal, Canada, the feasibility of using molten sulphur-dispersing surfactants to enhance the oxygen pressure leaching of chalcopyrite in the temperature range 125-155xc2x0 C. was investigated. The article concluded that most of the surfactants tested decomposed too rapidly to be of benefit. The best results were obtained with orthophenylenediamine (OPD) when it was added continuously during a test at fairly high dosage (50 kg/t). This resulted in significant increases in copper extraction, but only after prolonged retention times (6 hours). Chalcopyrite leached slowly even if molten sulphur was prevented from wetting the mineral surfaces. It was concluded the reaction rate is ultimately controlled by a passivating mechanism unrelated to elemental sulphur formation.
Despite all the known processes for the leaching of copper values from chalcopyrite, there is always a need for new processes of this type.
According to the invention there is provided a process for the extraction of copper from a copper sulphide containing concentrate, which comprises:
(a) dispersing finely divided copper sulphide containing concentrate having a P80 (80% of particles passing size) of from 5 micron to 20 micron inclusive in an aqueous sulphuric acid solution to form a slurry, the sulphuric acid being provided in an amount determined by the target copper, iron and acid concentration desired in a final leach solution;
(b) providing an effective amount of a suitable surfactant;
(c) reacting, with agitation, the slurry and surfactant with free oxygen bearing gas at an oxygen overpressure of from 100 kPa to 3000 kPa inclusive, preferably of from 400 kPa to 750 kPa inclusive, in a pressure vessel at a temperature of from 130xc2x0 C. to 160xc2x0 C. inclusive, to extract the copper values from the concentrate to produce the final leach solution containing dissolved copper values and a solid residue; and
(d) separating the final leach solution containing the dissolved copper values from the solid residue.
The final leach solution also contains other dissolved metal values. The final leach solution is then treated downstream to recover copper and other precious and base metal values.
The process is applicable to copper sulphide containing concentrates, the most important of which are those of the refractory chalcopyrite (CuFeS2); chalcocite (Cu2S); bomite (CuFeS4); and covellite (CuS), and the less abundant enargite (Cu2AsS4) or tetrahedrite (Cu12Sb4S13).
As indicated above, the sulphuric acid must be present in the slurry in an amount determined by the target copper, iron and acid concentration desired in the final leach solution, The acid to be added is determined relative to the elemental sulphur and sulphate yields required; sulphate is mainly in the form of copper sulphate, ferric sulphate and some ferrous sulphate. A stoichiometric amount of acid is required to ensure the required conversion, together with sufficient acid in the final leach solution to ensure target metal recoveries are maintained, The surfactant (or surface active agent) used may be any suitable surfactant, including organic compounds such as lignin derivatives, particularly calcium and sodium lignosulphonates; tannin compounds, particularly tree bark and heartwood extracts such as quebracho, hemlock and redwood extracts; orthophenylene diamine; and alkanyl sulphonates, particularly sodium alkylbenzene sulphonates, and mixtures of two or more thereof. The surfactant is preferably present in an amount of from 2 to 5 kg inclusive per tonne of concentrate.
The leaching reaction is carried out in an agitated pressure vessel at a temperature of from 130xc2x0 to 160xc2x0 C. inclusive and preferably at about 150xc2x0 C. Oxygen bearing gas is introduced into the pressure vessel (autoclave) to maintain an oxygen overpressure of from 100 kPa to 3000 kPa inclusive and preferably from 400 kPa to 750 kPa inclusive. Oxygen is preferred as the oxidising gas but oxygen enriched air may also be used.
It is to be noted that the process of the invention is carried out without the addition of an acidic halide solution.